Mercury cathode discharge tube



March 1940- T. JURRIAANSE in- AL 2,192,349

MERCURY CATHODE DISCHARGE TUBE Filed June 26, 1957 ,Q I I I, 13

l/Il/I/ Patented Mar. 5, 1940 UNITED STATES PATENT OFFEQE MERCURY CATHODE DISCHARGE TUBE Tom Jurriaanse and Johannes Gijsbertus Application June 26, 1937, Serial No. 150,624 In Germany July 8, 1936 9 Claims.

Our invention relates to mercury-cathode discharge tubes, and more particularly to anchoring the cathode spot of such tubes.

We shall describe our invention in connection with tubes having a metal envelope portion containing a mercury cathode; however it is not limited thereto but is also applicable to mercurycathode tubes of other constructions.

In such tubes a generally circular cathode-spot 10 anchoring body extending slightly from the surface of the mercury is commonly provided in the central portion of the mercury cathode, and in some cases a protective ring of a metal of poor anchoring properties, or of insulating material, intercepts the mercury surface between the anchoring body and tube wall to prevent the cathode-spot from passing over the surface of the mercury to the tube wall.

Under normal operating conditions the cathode spot adheres to the anchoring body and forms on the area'at which the mercury is in contact with the body, a line focus whose length is proportional to the intensity of the discharge path. However under some conditions, particu- 26 larly if the discharge current exceeds that value at which the line focus extends over the entire area of contact between the mercury and the anchoring body, the cathode spot may leave the anchoring body and rove over the mercury sur- 30 face in the well-known and undesired manner and may even reach the tube wall. This is due to the fact that in such prior constructions it is possible for the cathode spot, during its rapid movement over the mercury surface, to traverse considerable paths before it can again settle on the anchoring body.

The object of our invention is to overcome the above difiicuities, and to provide a'construction which makes it very diflicult for the cathode spot tomove any substantial distance over the mercury surface without finding an opportunity of anchoring.

According to the invention, we provide such cathodes with one or more additional members having at least a metallic edge of good anchoring properties, and so arrange the same thatthe distance over the surface of the mercury between the anchoring body and these members, or between the members themselves, is small.

50 With such constructions the possibility of the cathode spot anchoring is greatly increased and additional obstacles are placed in the path of the cathode spot over the mercury surface to the tube wall, whereas the small distances be- 55 tween potential anchoring points greatly reduces the possibilities of the cathode spot roving over the surface of the mercury.

As the cathode spot travels over the mercury surface at a speed of about 10 meters per sec end-thus about 10 cms. in 0.01 sec., which is i about the time between two rectified pulsations of cycle currentthe anchoring members should be so disposed that the cathode spot has several opportunities of anchoringeven Within 0.01 sec. For this purpose we prefer to make this distance w of the order of 1 cm.

In order that our invention may be clearly understood and readily carried into effect, we shall describe the same more fully with reference to the accompanying drawing, in which: 1

Figure 1 is a sectional view of a mercurycathode discharge tube embodying the invention, and

Fig. 2 is a sectional view of a portion of Figure 1 and illustrates another embodiment of the invention.

The rectifier shown in Figure 1 has an envelope comprising a cup-shaped metal member I, for instance of chrome iron, and a glass member 2 hermetically fused together at H. Disposed in the bottom of member I is a mercury cathode 3, whereas a main anode 8 is supported from the lower end of a conductor 6 whose upper end is secured to a metal disc'4 hermetically sealed in lass portion 2 and carrying a suitable terminal. 30 Supported from conductor 6 and surrounding anode 8 is a' cylindrical screen it serving to protect the higher internal surfaces of portion l and seal I! from the detrimental effects of the discharge.

Supported by screen I l which is preferably of sheet molybdenum. is an insulating tube 2!! through the bore of which extends a conductive rod i9 carrying on its lower end an auxiliary anode 9 adapted to be moved in the direction of the double-headed arrow. For this purpose, the upper end of rod i9 carries a plunger l8 of magnetic material electrically connected through compression a spring 22 to a core 2! of a magnetic material. Core 2| is supported from the 45 lower end of a conductive rod 1 secured to a disc 5 hermetically sealed in glass portion 2. Outside the envelope and surrounding core 2| is coil l0 which serves to raise anode 9 from the surface of the mercury. 5

Surrounding the metal number I is a cooling jacket l2 having an inlet opening 13 and an outlet opening M, and through which a circulating cooling medium, such as water, is circulated in the direction of the arrows during operation 1 other.

of the rectifier. Jacket I3 is secured to metal member I by a copper bolt l5 secured, for instance by welding, to the bottom of member I and serving to supply current to cathode 3. Secured to the upper surface of the bottom of memher I is a cathode-spot anchoring member 25, for instance of nickel. Surrounding member 25 is a ring 25 of a metal of poor anchoring properties, such as iron or molybdenum, which serves to prevent the cathode spot from reaching the wall of the tube.

In accordance with the invention, a ring 21 having at least its inner edge portion of'a metal of good anchoring properties, for instance of nickel, surrounds anchoring body 25 and provides an additional anchoring means. The distance between body 25 and ring 21 is made relatively small and of the order of 1 cm., whereas rings 26 and 2'! are provided with recesses 29 and 36.

respectively, to permit the condensed mercury flowing down the tube wall to return to the space within the rings.

We prefer to form the ring 27 from nickel, as this metal is inexpensive, has excellent anchoring properties and is substantially unattacked by the mercury and the cathode spot. This prevents reduction in tube life by premature destruction of ring 21.

Only a single ring 21' has been shown in Figure 1; however a plurality of such rings may be used depending upon the size of the mercury cathode. In this case however all of the rings, except the outmost one, have to be provided with passageways through which the resulting concentric mercury surfaces are connected to each In some cases it is advantageous to unite rings 25 and 21 to form a bimetallic ring which is made internally with a material having satisfactory anchoring properties and externally with material having poor anchoring properties.

Such a construction is illustrated in Figure 2 in which a bimetallic ring 32 is formed of an internal ring of nickel and an external ring 34 of molybdenum. These rings are provided with recesses 35 which serve the same purpose as recesses 29 and 3B of Figure 1.

It will be noted that the cathode spot has an excellent opportunity of anchoring both internally and externally in the annular space formed between body 25 and ring 32. However, the annular space between ring 32 and the vessel 1 is deliberately made small, for example a few mms, and as it is bounded by surfaces of materials of poor anchoring properties, the discharge is practically prevented from settling therein.

Anchoring members of annular shape are most convenient, particularly for comparatively small cathodes, because they may readily be manufactured. and yield a completely sufficient anchoring length for the current intensities usually employed.

While we have described our invention with reference to specific examples and applications, we do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is:

1. A discharge tube comprising an envelope, an anode, a mercury cathode, a cathode-spot anchoring body extending during operation of the tube above the surface of the mercury to form a cathode line between its lateral surface and the mercury surface, and means to confine the cathode spot to a portion of the mercury surface comprising a member encircling said body and extending with a metallic surface of good anchoring properties above the surface of the mercury at any height of the mercury level 00- curring under operating conditions of the tube,

mercury to form a cathode line between its lateral surface and the mercury surface, and means to confine the cathode spot to a portion of the mercury surface comprising a member encircling said body and extending substantially to ,l the height of said body with a metallic surface of good anchoring properties, said body and member bounding a narrow portion of the active I cathode surface. 7

3. A discharge tube comprising an envelope, an

anode, a mercury cathode, a cathode-spot anch'oring body extending during operation of the tube above the surface of the mercury to form a tending above the surface of. the mercury with a I metallic surface of good anchoring properties at;

any height of the mercury level occurring under operating conditions of the tube, said body. and

member bounding an active cathode tion having a width of about 1 cm.

4. A discharge tube comprising an envelope,

an anode, a mercury cathode, a cathode-spot anchoring body extending during operation of the tube above the surface of the mercury to form a cathode line between its lateral surface and the mercury surface, and means to; confine the cathode spot to a portion of the mercurysur-- face comprising a member encircling said body and extending above the surface of the mercury with a metallic surface of good anchoring propj erties at any height of they mercuryKlevel occurring under operating conditions of the tube, said body and member bounding a curved narrow portion of the active cathode surface. l

5. A discharge tube comprising an envelope, an anode, a mercury cathode, a cathode-spot anchoring body extending during operation of the tube above the surfaceof the mercury to form a cathode line between its lateral surface and the mercury surface, and means to confine'the cathode spot to a narrow portion of the mercury surface comprising a plurality of annular members encircling said body and each extending above thesurface of the mercury with a metallic surface of good anchoring properties at any height of the mercury level occurring under operatingconditions of the tube, said body and members dividing the active cathode surface into a plurality of narrow annular strips and being individually connected in good heat-transferring relationship with the envelope.

6. A discharge tube comprising an envelope,

an anode, a mercury cathode, a cathode-spot ansurface porchoring body extending during operation of the tube above the surface of the mercury to form a cathode line between its lateral surface and'the mercury surface, and means to confine the oathode spot to a portion of the mercury surface comprising a member encircling said body and extending with a nickel surface above the surface of the mercury at any height of the mercury level occurring under operating conditions of the tube, said body and member bounding a narrow portion of the active cathode surface.

7. A discharge tube comprising an envelope, an anode, a mercury cathode, a cathode-spot anchoring body, and a composite member surrounding said body and extending slightly from the surface of the mercury, said member having an internal metallic surface of good anchoring properties and an external surface of poor anchoring properties.

8. A discharge tube comprising an envelope having a cup-shaped portion, an anode, a mercury cathodewithin said portion, a cathode-spot anchoring body extending slightly from the surface of said mercury, and a composite ring surrounding said body and slightly extending from the surface of said mercury, said ring being closely spaced from the walls of said cup-shaped portion and comprising an inner ring of nickel and anouter ring of a material of poor anchoring properties.

9. A discharge tube comprising an envelope having a cup-shaped metal portion, an anode, a mercury cathode within said portion, a cathode-spot, anchoring body extending from the surface of the mercury cathode, and a composite ring surrounding said body and closely spaced from the surface of said metal portion, said ring extending slightly from the surface ofthe mercury cathode and comprising an inner ring of metal of good anchoring properties and an outer ring, of a metal of poor anchoring properties.

TOM JURRIAANSE. 4 JOHANNES GIJSBERTUS WILI-IELM MULDER. 

